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CHARACTERIZATION OF ROOT AGRAVITROPISM INDUCED BY GENETIC, CHEMICAL, AND DEVELOPMENTAL CONSTRAINTS
Author(s) -
Moore Randy,
Fondren W. Mark,
Marcum Heidi
Publication year - 1987
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1987.tb08615.x
Subject(s) - gravitropism , amyloplast , biology , biophysics , root cap , curvature , elongation , botany , auxin , mutant , biochemistry , plastid , arabidopsis , geometry , gene , mathematics , chloroplast , materials science , shoot , ultimate tensile strength , meristem , metallurgy
The patterns and rates of organelle redistribution in columella (i.e., putative statocyte) cells of agravitropic agt mutants of Zea mays are not significantly different from those of columella cells in graviresponsive roots. Graviresponsive roots of Z. mays are characterized by a strongly polar movement of 45 Ca 2+ across the root tip from the upper to the lower side. Horizontally‐oriented roots of agt mutants exhibit only a minimal polar transport of 45 Ca 2+ . Exogenously‐induced asymmetries of Ca result in curvature of agt roots toward the Ca source. A similar curvature can be induced by a Ca asymmetry in normally nongraviresponsive (i.e., lateral) roots of Phaseolus vulgaris. Similarly, root curvature can be induced by placing the roots perpendicular to an electric field. This electrotropism increases with 1) currents between 8–35 mA, and 2) time between 1–9 hr when the current is constant. Electrotropism is reduced significantly by treating roots with triiodobenzoic acid (TIBA), an inhibitor of auxin transport. These results suggest that 1) if graviperception occurs via the sedimentation of amyloplasts in columella cells, then nongraviresponsive roots apparently sense gravity as do graviresponsive roots, 2) exogenously‐induced asymmetries of a gravitropic effector (i.e., Ca) can induce curvature of normally nongraviresponsive roots, 3) the gravity‐induced downward movement of exogenously‐applied 45 Ca 2+ across tips of graviresponsive roots does not occur in nongraviresponsive roots, 4) placing roots in an electrical field (i.e., one favoring the movement of ions such as Ca 2+ ) induces root curvature, and 5) electrically‐induced curvature is apparently dependent on auxin transport. These results are discussed relative to a model to account for the lack of graviresponsiveness by these roots.